Probably more than you wanted to know. :p Think about how older EIDE and PATA133 are interchangeable but older stuff isn't as fast. In your case, older stuff should transfer at exactly half the speed.
SATA II Misnomer
The 3.0 Gbit/s specification has been very widely referred to as “Serial ATA II” (“SATA II” or “SATA2“), contrary to the wishes of the The Serial ATA International Organization (SATA-IO) which defines the standard.
The term SATA II has grown in popularity, causing great confusion with customers because, quite simply, it’s a misnomer.
The first step toward a better understanding of SATA is to know that SATA II is not the brand name for SATA’s 3Gb/s data transfer rate, but the name of the organization formed to author the SATA specifications. The group has since changed names, to the Serial ATA International Organization, or SATA-IO.
The 3Gb/s capability is just one of many defined by the former SATA II committee, but because it is among the most prominent features, 3Gb/s has become synonymous with SATA II, hence the source of the confusion.